This invention relates to a device which prevents the freezing of a reciprocating air motor which drives a reciprocating plunger pump for liquid pressurized transport.
Conventional reciprocating air motors function by using compressed air as the drive source and release compressed air into the atmosphere at each pump stroke. A liquid pump (which picks up liquid and moves it under compression to the target site) is usually connected to such air motors at the bottom. An air motor is used in order to drive the liquid pump and usually operates at 50 or fewer strokes per minute.
The air motor consists of three principal parts, an air cylinder, air piston and a compressed air switch valve. The air piston rises or falls within the cylinder through the action of compressed air, and the direction of the moving stroke is reversed through actuation of the switch valve at the end of the stroke. The compressed air within the air cylinder is released into the atmosphere at this time, but the exhaust passage and the compressed air switch valve are usually cooled to a temperature of less than -30 degrees C. because of the phenomenon of adiabatic expansion during exhaust. Since moisture is usually present in the air which is supplied and in the air within the air motor, that humidity is turned into ice flakes at each incident of cooling brought about by exhaust, and the ice flakes adhere to each section within the exhaust passage and the air motor, and build up. Foaming resin can be attached to the inside of the air motor cover in order to reduce the noise during exhaust.
However, when ice flakes of humidity in the atmosphere accompanying the aforementioned exhaust form in such conventional airdriven air motors, they readily deposit and accumulate on the exhaust passage and on the compressed air switch valve. This phenomenon occurs within a short period of time when there is a large amount of humidity in the air which is supplied or when the operating speed of the air motor is fast. As a result, the exhaust passage is constricted by the ice flakes which deposit, thereby reducing the amount of exhaust air, making operation of the air motor irregular. Moreover, the switching operations are restricted by the ice depositing on the compressed air switch valve and this can stop operation of the air motor. The exhaust passage can be blocked by ice deposits, leading to the inability to operate the air motor. The countermeasure has been to adequately heat the supplied air to avoid the forming of ice, but a vast amount of thermal energy is required for adequate heating since the amount of air supplied to the air motor is usually great. This necessitates vast expenditures for heating equipment.